package com.cgmnx.admin.common.exception;


/**
 *
 */
public class Preconditions {

    private Preconditions() {
    }


    public static void checkArgument(
            boolean expression, Object errorMessage) {
        if (!expression) {
            throw new CgmnxException(String.valueOf(errorMessage));
        }
    }

    /**
     * Ensures the truth of an expression involving one or more parameters to the
     * calling method.
     *
     * @param expression           a boolean expression
     * @param errorMessageTemplate a template for the exception message should the
     *                             check fail. The message is formed by replacing each {@code %s}
     *                             placeholder in the template with an argument. These are matched by
     *                             position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
     *                             Unmatched arguments will be appended to the formatted message in square
     *                             braces. Unmatched placeholders will be left as-is.
     * @param errorMessageArgs     the arguments to be substituted into the message
     *                             template. Arguments are converted to strings using
     *                             {@link String#valueOf(Object)}.
     * @throws cgmnxException if {@code expression} is false
     * @throws cgmnxException if the check fails and either {@code
     *                        errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
     *                        this happen)
     */
    public static void checkArgument(boolean expression,
                                     String errorMessageTemplate,
                                     Object... errorMessageArgs) {
        if (!expression) {
            throw new CgmnxException(
                    format(errorMessageTemplate, errorMessageArgs));
        }
    }

    /**
     * Ensures that an object reference passed as a parameter to the calling
     * method is not null.
     *
     * @param reference    an object reference
     * @param errorMessage the exception message to use if the check fails; will
     *                     be converted to a string using {@link String#valueOf(Object)}
     * @return the non-null reference that was validated
     * @throws CgmnxException if {@code reference} is null
     */
    public static <T> T checkNotNull(T reference, Object errorMessage) {
        if (reference == null) {
            throw new CgmnxException(String.valueOf(errorMessage));
        }
        return reference;
    }

    /**
     * Ensures that an object reference passed as a parameter to the calling
     * method is not null.
     *
     * @param reference            an object reference
     * @param errorMessageTemplate a template for the exception message should the
     *                             check fail. The message is formed by replacing each {@code %s}
     *                             placeholder in the template with an argument. These are matched by
     *                             position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
     *                             Unmatched arguments will be appended to the formatted message in square
     *                             braces. Unmatched placeholders will be left as-is.
     * @param errorMessageArgs     the arguments to be substituted into the message
     *                             template. Arguments are converted to strings using
     *                             {@link String#valueOf(Object)}.
     * @return the non-null reference that was validated
     * @throws CgmnxException if {@code reference} is null
     */
    public static <T> T checkNotNull(T reference,
                                     String errorMessageTemplate,
                                     Object... errorMessageArgs) {
        if (reference == null) {
            // If either of these parameters is null, the right thing happens anyway
            throw new CgmnxException(
                    format(errorMessageTemplate, errorMessageArgs));
        }
        return reference;
    }


    /**
     * Substitutes each {@code %s} in {@code template} with an argument. These
     * are matched by position - the first {@code %s} gets {@code args[0]}, etc.
     * If there are more arguments than placeholders, the unmatched arguments will
     * be appended to the end of the formatted message in square braces.
     *
     * @param template a non-null string containing 0 or more {@code %s}
     *                 placeholders.
     * @param args     the arguments to be substituted into the message
     *                 template. Arguments are converted to strings using
     *                 {@link String#valueOf(Object)}. Arguments can be null.
     */
    private static String format(String template,
                                 Object... args) {
        template = String.valueOf(template); // null -> "null"

        // start substituting the arguments into the '%s' placeholders
        StringBuilder builder = new StringBuilder(
                template.length() + 16 * args.length);
        int templateStart = 0;
        int i = 0;
        while (i < args.length) {
            int placeholderStart = template.indexOf("%s", templateStart);
            if (placeholderStart == -1) {
                break;
            }
            builder.append(template.substring(templateStart, placeholderStart));
            builder.append(args[i++]);
            templateStart = placeholderStart + 2;
        }
        builder.append(template.substring(templateStart));

        // if we run out of placeholders, append the extra args in square braces
        if (i < args.length) {
            builder.append(" [");
            builder.append(args[i++]);
            while (i < args.length) {
                builder.append(", ");
                builder.append(args[i++]);
            }
            builder.append(']');
        }

        return builder.toString();
    }
}